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Astrophysics > Astrophysics of Galaxies

Title:
Inside the Bondi radius of M87

Abstract: Chandra X-ray observations of the nearby brightest cluster galaxy M87 resolve
the hot gas structure across the Bondi accretion radius of the central
supermassive black hole, a measurement possible in only a handful of systems
but complicated by the bright nucleus and jet emission. By stacking only short
frame-time observations to limit pileup, and after subtracting the nuclear PSF,
we analysed the X-ray gas properties within the Bondi radius at 0.12-0.22 kpc
(1.5-2.8 arcsec), depending on the black hole mass. Within 2 kpc radius, we
detect two significant temperature components, which are consistent with
constant values of 2 keV and 0.9 keV down to 0.15 kpc radius. No evidence was
found for the expected temperature increase within ~0.25 kpc due to the
influence of the SMBH. Within the Bondi radius, the density profile is
consistent with $\rho\propto r^{-1}$. The lack of a temperature increase inside
the Bondi radius suggests that the hot gas structure is not dictated by the
SMBH's potential and, together with the shallow density profile, shows that the
classical Bondi rate may not reflect the accretion rate onto the SMBH. If this
density profile extends in towards the SMBH, the mass accretion rate onto the
SMBH could be at least two orders of magnitude less than the Bondi rate, which
agrees with Faraday rotation measurements for M87. We discuss the evidence for
outflow from the hot gas and the cold gas disk and for cold feedback, where gas
cooling rapidly from the hot atmosphere could feed the cirumnuclear disk and
fuel the SMBH. At 0.2 kpc radius, the cooler X-ray temperature component
represents ~20% of the total X-ray gas mass and, by losing angular momentum to
the hot gas component, could provide a fuel source of cold clouds within the
Bondi radius.